This non-provisional application claims priority under 35 U.S.C. §119(a) on Korean Patent Application No. 2005-11290 filed on Feb. 7, 2005, which is herein incorporated by reference.
1. Field of the Invention
Embodiments of the present invention relate, generally, to nonvolatile nanochannel memory using a mesoporous material, and more particularly, to a memory device comprising a mesoporous material able to form nanochannels, in which a memory layer having metal nanoparticles or metal ions fed into the nanochannels is disposed between an upper electrode and a lower electrode.
2. Description of the Related Art
With the rapid development of the information and communication industries, the demand for various memory devices has drastically increased. In particular, memory devices required for portable terminals, various smart cards, electronic money, digital cameras, games, MP3 players, etc. must be nonvolatile so that the recorded information is not lost even when no power is consumed.
As techniques for large scale integration (LSI) have been developed, the number of bits of memory integrated in IC chips reaches the level of megabits, and thus, line and space widths having sub-micrometer sizes are required. Although almost all conventional nonvolatile memory devices are manufactured using standard silicon technology, the silicon based device thus manufactured has shortcomings, such as a complicated structure and a large sized single memory cell, and high capacity thereof cannot be realized. In order to manufacture silicon based memory having a high memory capacity with high integration, a fining process capable of decreasing line and space widths per unit area should be performed. This increases process costs and results in high costs of manufacturing memory chips. Moreover, the manufacturing techniques of the chips make it difficult to further miniaturize the chips, and hence, profitability problems are now being faced.
Therefore, vigorous attempts have been made to develop next-generation memory devices, which have ultrahigh speeds, high capacities and low power consumption suitable for the development of portable information and communication systems and apparatuses to wirelessly handle large amounts of information, instead of conventional memory devices. The next-generation memory devices include, for example, ferroelectric RAM, magnetic RAM, phase change RAM, nanotube RAM, holographic memory, organic memory, etc., depending on the kind of material constituting a unit cell in a semiconductor. Of these memory devices, organic memory achieves memory capability, using bistable resistance values obtained by applying voltage to an organic material provided between upper and lower electrodes. Thus, the organic memory can overcome the problems of processability, manufacturing costs and integration regarded as disadvantages of conventional flash memory, while unchangedly exhibiting the nonvolatile characteristics which are the advantage of flash memory. Therefore, organic memory is widely expected to be the next-generation memory technology.
In this regard, Potember, USA, in 1979, first reported a memory phenomenon, as well as electrical switching at a speed on the nano-second scale, using CuTCNQ (7,7,8,8-tetracyano-p-quinodimethane) as a charge transfer complex containing an organic metal [Appl. Phys. Lett., 34 (1979) 405]. Japanese Patent Laid-open Publication No. Sho. 62-956882 discloses an electrical memory device using CuTCNQ. However, the above memory device can be manufactured only by thermal deposition using an expensive evaporator, instead of a simple process such as spin coating, due to the use of the monomer, and hence, has no advantage in terms of processability.
As an organic material showing electrical bistability upon the application of an electrical field, conductive polymers other than a charge transfer material are also known [Thin Solid Film, 446 (2004) 296-300]. In addition, memory properties obtained by using a phthalocyanin based compound as an organic dye have been reported [Organic Electronics, 4(2003) 3944]. In addition, switching/memory properties due to conformational change under oxidation-reduction and electrical field are known [Applied Physics Letter, 82 (2003) 1215].
U.S. Pat. App. Pub. Serial No. 2002-163057 discloses a semiconductor device including a middle layer made of a mixture comprising an ionic salt such as NaCl or CsCl and a conductive polymer, interposed between upper and lower electrodes. Such a device manifests switching/memory properties using charge separation under an electrical field. Although the conductive polymer may be used for spin coating, its molecular weight and distribution are difficult to accurately control. Thus, reproducibility of the material is problematic, and uniform performance of the device cannot be realized.
In addition, U.S. Pat. No. 6,055,180 discloses a memory device using ferroelectricity depending on a crystalline phase of a fluorine based polymer, such as poly(vinyldifluoroethylene). However, the fluorine based polymer is difficult to apply due to hydrophobic properties of fluorine, thus having decreased processability. Also, the above patent is disadvantageous in that because the information may be recorded only once, and the stored information may be optically read, the size of the device increases and the structure thereof becomes complicated.
In addition, U.S. Pat. App. Pub. Serial No. 2003-166602 discloses a memory device including an active layer in which a plurality of nanochannels or pores for use in charge transfer are present, without the need of a conventional semiconductor material. However, the above device has a complicated structure, since the charge transfer path is formed of a polymer material and an inactive layer for supplying ions must be present along with the active layer to change the electrical conductivity of the active layer.
Further, a memory device manufactured by Y. Yang who is a professor at UCLA, USA, by positioning thin metal nanoclusters between two organic layers has been reported to have excellent memory properties, which may be understood based on the change of the overall resistance of the device via charge/discharge of the metal nanoclusters functioning as a capacitor, or based on an MIM (Metal/Insulator/Metal) memory phenomenon proposed by J. G. Simmons and R. R. Verderber. In addition, IBM has manufactured a memory device exhibiting an MIM memory phenomenon, using gold particles dispersed in a polymer. As such, the above memory device is characterized in that the gold particles function as a current flow channel.
As mentioned above, the conventionally used organic material having bistability is disadvantageous because it is deposited only by thermal deposition using an expensive evaporator, instead of a simple process such as spin coating, due to the use of the monomer. The conductive polymer may undergo spin coating, however accurate molecular weight and distribution thereof are difficult to obtain. Thus, the reproducibility of the material is problematic, resulting in nonuniform performance of the device. In the cases where the metal nanoparticles are deposited into a layer between the organic materials or are dispersed in the polymer, the current flow paths become random and thus are incontrollable, consequently obtaining poor reproducibility and nonuniform performance.